Nearly any new development of land must incorporate a system for managing water run-off from the developed land. Current regulatory schemes typically require developers to install underground water detention and/or retention systems that effectively maintain a flow of water into and off of the developed land that mimics the natural (i.e., pre-development) flow from the land.
Such systems typically are installed under large concrete or asphalt surfaces and often must be capable of bearing highly variable weight loads (e.g., a parking lot). Ideally, such systems should maximize water storage while occupying as small a “footprint” as possible in order to minimize land usage.
In addition, urban and suburban landscapes generate a variety of contaminants that can enter storm water, polluting downstream receiving waters. Many regulatory schemes require not only controlling water run-off, but also water quality. Typically, developed land accumulates pollutants that can contaminate water run-off, particularly after storms. The entrance of gross pollutants, such as trash, debris and coarse sediments, into typical storm water filtration systems is known to reduce efficiency, increase maintenance frequency of the storm water filtration systems, and escalate the costs.
Ideally, underground water management systems should pre-treat water flow from the developed land prior to releasing it. Pre-filtration systems may be used to separate and retain gross pollutants from the filtering systems. They also can be used to capture and retain sediment, oils, metals, and other constituents found in storm water. Such pre-filtration systems should be incorporated into the underground water retention or detention system to minimize land usage, but also should be accessible for intermittent cleaning, repair, and/or other maintenance.
Generally, large (normally pre-cast concrete) pre-filtration structures are installed next to or along the side of the underground water detention or retention system. The pre-filtration structures are connected to the underground water detention or retention system by piping. This type of pre-filtration structure requires additional material and labor costs. It also requires the use of more space to accommodate the pre-treatment structure that sits next to or along the side of the underground water detention or retention system.